1. Field of the Invention
The present invention relates to a semiconductor memory device having a ferroelectric capacitor and a method of manufacturing the same.
2. Description of the Related Art
In recent years, a nonvolatile memory using a ferroelectric capacitor (FeRAM), as disclosed in, for example, Jpn. Pat. KOKAI Publication No. 10-255483, attracts attentions as one of semiconductor memory devices.
The memory cell of the FeRAM is constructed, for example, as follows. Specifically, a gate electrode is formed on a semiconductor substrate and a pair of source/drain diffusion layers is formed in surface region of the semiconductor substrate in a manner to have the gate electrode sandwiched therebetween, thereby forming a transistor. An interlayer insulating layer is formed on the transistor, and a first contact connected to one of the source/drain diffusion layers of the transistor is formed in the interlayer insulating layer. A second contact is formed on the first contact, and a ferroelectric capacitor including a lower electrode, a ferroelectric film and an upper electrode is connected to the second contact.
In the conventional structure described above, the ferroelectric capacitor is formed first, followed by forming the second contact connected to the first contact. Therefore, it is known to the art that, if an opening for the second contact is formed on the first contact, damage is done to the ferroelectric capacitor. In order to overcome the damage done to the ferroelectric capacitor, it is necessary to carry out a heat treatment under a high temperature after formation of the opening for the second contact.
However, the first contact is formed of a material that is easily oxidized such as W (tungsten). Therefore, if an oxygen annealing is carried out under a high temperature in order to overcome the damage done to the ferroelectric capacitor, the first contact is oxidized, with the result that it was impossible to carry out an oxygen annealing under a high temperature. Such being the situation, it was impossible to overcome completely the damage done to the ferroelectric capacitor, leading to reduction of the yield.